This relates generally to a laser transmitter and, more particularly, to a laser reference system and method of orienting a reference plane of laser light generated by a laser transmitter. The laser transmitter is effectively aligned so that the laser transmitter defines a plane having desired slopes in desired alignment directions. The alignment directions need not be orthogonal.
Laser light systems have been employed in numerous prior art surveying and construction applications. In one type of system, a laser light transmitting device provides a rotating laser beam which establishes a reference plane over a work site. Typically, the reference plane creates either a horizontal elevation reference plane, or an appropriately tilted reference plane. The laser light is detected by one or more laser beam detectors. The laser beam detectors are mounted on supports placed at considerable distances from the transmitting device or on construction equipment that is operated at the work site.
Prior to operation, it is necessary to set up the transmitting device at the work site in proper orientation to the work site. As an example, assume that an architect has previously determined that the work site is to slope in a certain direction at a certain grade. Assume further that the work site is rectangular, and that a corner of the work site is selected as the origin of a coordinate system, with one edge of the rectangle being the x-axis and the other edge of the rectangle being the y-axis. The desired fall line may extend in a direction between the x-axis and y-axis. The architect will have specified an x-axis slope and a y-axis slope for the work site that together produce the desired slope along the fall line.
The transmitter is placed at the corner of the work site that constitutes the origin. The transmitter has its own internal x-axis and y-axis, and these are marked on the top of the transmitter. The operator manually lines up the transmitter x and y axes with the work site x and y axes using these markings, or using a telescope that may be mounted on the top of the transmitter for this purpose. Neither of these arrangements for aligning a transmitter permits great precision.
If the transmitter is perfectly aligned such that its x-axis and its y-axis are parallel to the x-axis and y-axis of the work site, respectively, then when the operator inputs the x-axis grade and the y-axis grade, the transmitter will produce a reference plane of light having the correct pitch along the fall line. A problem develops, however, when the x-axis and the y-axis of the transmitter are misaligned, i.e., pivoted slightly clockwise or counterclockwise, as seen from above, with respect to the x-axis and y-axis of the work site. If the transmitter is misaligned and if the operator inputs the desired work site axes slopes, the transmitter will produce a reference light plane having the correct pitch, but the maximum pitch of the reference plane will not be aligned with the desired fall line. Instead, the reference plane will be rotated slightly about a vertical axis from the orientation that is desired.
One system for aligning a transmitter to a work site is shown in U.S. Pat. No. 6,055,046, issued Apr. 25, 2000, to Cain. The system has a transmitter that includes an angle encoder. The angle encoder continuously indicates the angular orientation of the rotating beam. The transmitter and a retroreflective target are positioned along a side of the work site, spaced apart in the direction to which the laser transmitter is to be aligned. The angular orientation of the target is then determined by the angle encoder output when light is reflected from the target back to the transmitter. Alternatively, an electro-optical detector may be used with the detector, sending a signal via a radio or other transmitter back to a receiver on the transmitter when the beam is detected. In either event, the transmitter axes are rotated into alignment electronically. This arrangement requires an accurate angle encoder, thus adding to the expense and complication in the construction of the device.
Another system for aligning a transmitter, shown in U.S. Pat. No. 6,693,706, issued Feb. 17, 2004, to Kahle, determines the amount of transmitter misalignment about a vertical axis (termed “the rake angle”) and then compensates for it. Stated another way, the grade rake angle is the angular misalignment (as seen from above) of the x and y axes of the transmitter, and the x and y axes of the work site, respectively. This system determines this rake angle and alters the operation of the transmitter such that a properly oriented reference plane is produced.
These prior art systems were limited to determining and compensating for alignment directions that are orthogonal, such that the x-axis and the y-axis of the transmitter, which are also orthogonal, will be offset from the alignment directions by the same rake angle. This is not always the case, however. Furthermore, it may sometimes be desirable to match a grade defined by the transmitter and two beam detectors, and then determine the inclination of the matched grade in the two alignment directions. Accordingly, it is seen that there is a need for an improved and simplified system for aligning a laser transmitter to a work site, such that a plane of laser light projected from the laser transmitter accurately defines a reference plane with a properly oriented slope.